1. Field of the Invention
Embodiments of the invention generally relate to electrochemical plating systems, and in particular, anodes for electrochemical plating systems.
2. Description of the Related Art
Metallization of sub-quarter micron sized features is a foundational technology for present and future generations of integrated circuit manufacturing processes. More particularly, in devices such as ultra large scale integration-type devices, i.e., devices having integrated circuits with more than a million logic gates, the multilevel interconnects that lie at the heart of these devices are generally formed by filling high aspect ratio (greater than about 4:1, for example) interconnect features with a conductive material, such as copper or aluminum, for example. Conventionally, deposition techniques such as chemical vapor deposition (CVD) and physical vapor deposition (PVD) have been used to fill these interconnect features. However, as the interconnect sizes decrease and aspect ratios increase, void-free interconnect feature fill via conventional metallization techniques becomes increasingly difficult. As a result thereof, plating techniques, such as electrochemical plating (ECP) and electroless plating, for example, have emerged as viable processes for void free filling of sub-quarter micron sized high aspect ratio interconnect features in integrated circuit manufacturing processes.
In an ECP process, for example, sub-quarter micron sized high aspect ratio features formed into the surface of a substrate may be efficiently filled with a conductive material, such as copper, for example. ECP plating processes are generally two stage processes, wherein a seed layer is first formed over the surface features of the substrate, and then the surface features of the substrate are exposed to an electrolyte solution, while an electrical bias is simultaneously applied between the substrate and a copper anode positioned within the electrolyte solution. The electrolyte solution is generally rich in ions to be plated onto the surface of the substrate, and therefore, the application of the electrical bias causes these ions to be urged out of the electrolyte solution and to be plated onto the seed layer.
An ECP plating solution generally contains several constituents, such as, for example, a copper ion source, which may be copper sulfate, an acid, which may be sulfuric or phosphoric acid and/or derivatives thereof, a halide ion source, such as chlorine, and one or more additives configured to control various plating parameters. Additionally, the plating solution may include other copper salts, such as copper fluoborate, copper gluconate, copper sulfamate, copper sulfonate, copper pyrophosphate, copper chloride, or copper cyanide, for example. The solution additives, which may be, for example, levelers, inhibitors, suppressors, brighteners, accelerators, or other additives known in the art, are typically organic materials that adsorb onto the surface of the substrate being plated. Useful suppressors typically include polyethers, such as polyethylene glycol, or other polymers, such as polyethylene-polypropylene oxides, which adsorb on the substrate surface, slowing down copper deposition in the adsorbed areas. Useful accelerators, which are often not organic in nature, typically include sulfides or disulfides, such as bis(3-sulfopropyl) disulfide, which compete with suppressors for adsorption sites, accelerating copper deposition in adsorbed areas. Useful levelers typically include thiadiazole, imidazole, and other nitrogen containing organics. Useful inhibitors typically include sodium benzoate and sodium sulfite, which inhibit the rate of copper deposition on the substrate.
One challenge associated with ECP systems is that several of the components/constituents generally used in plating solutions are known to react with the surface of the copper anode forming what is generally known as anode sludge. Additionally, copper anodes in ECP systems are prone to upper surface dishing, i.e., the central portion of an annular anode generally erodes faster than the perimeter, and therefore, the anode sludge accumulates in the dished out portion of the anode. Although electrolyte flow over the surface of the anode has conventionally been used to flush sludge from the surface of the anode, conventional apparatuses and flow rates have not been effective in transporting the anode sludge away from the anode surface. The accumulation of anode sludge is known to inhibit copper dissolution from the anode into the plating solution, and therefore, may affect the copper ion concentration in the plating solution, and as a result thereof, detrimentally affect the plating characteristics.
Therefore, there is a need for an apparatus and method for electrochemically plating copper, wherein the apparatus and method includes an anode configured to remove anode sludge therefrom during plating operations.